Suspended acoustic rafts explained

 

Have you ever wondered what suspended acoustic rafts are and how they acoustically work?

This page briefly explains:

  • what suspended acoustic rafts are exactly
  • which sound absorption performances acoustic rafts achieve and, most importantly, how they should be specified
  • which materials are usually used for acoustic rafts
  • examples of acoustics rafts products available on the market
 

 

Are you looking to understand how acoustic products work and find examples available on the market? 

Visit the Acoustic Design Catalogue by clicking on the button below.

 

What are suspended acoustic rafts?

Suspended acoustic rafts are free-hanging and flat elements made with a thick fibrous or porous materials that have sound absorption qualities. You hang them horizontally at a certain distance from a hard surface (usually a soffit).

They are a popular option to reduce the sound reverberation in:

  • education spaces
  • office spaces
  • assembly spaces
  • public spaces (such as receptions, entrance halls, etc)

 

Brief description of suspended acoustic raft systems

Suspended acoustic rafts - sound absorption - acoustic absorption - acoustic consultant - acoustic design - architectural acoustic design

Although acoustic rafts are mostly square or rectangular, some of them are also roundoval or any other bespoke shape.

Some raft manufacturers/suppliers give the option to include lighting and other electrical systems within the rafts.

 

Sound absorption performance of suspended acoustic rafts

The sound absorptive materials used for suspended acoustic rafts generally achieve sound absorption Class AClass B or Class C.

However, you should know that sound absorption classes are generally for a materials fixed to a hard surface with only one side visible. This side is the only one that absorbs sound. The other one doesn’t.

For acoustic rafts, it is a little bit different.

 

Suspended acoustic rafts – Sound absorption below and above

Not only the underside of the rafts absorbs sound, but also upper side indirectly.

Sound will first hit the hard surface above the acoustic rafts and then the upper side of the rafts.

Therefore, the distance between the rafts and the hard surface above has an influence on the sound absorption of the raft systems. Below approximately 1m, the further the rafts from the hard surface, the higher the sound absorption at mid and high frequencies.

 

Sound absorption below and above the rafts

sound absorption below and above the rafts - Suspended acoustic rafts - sound absorption - acoustic absorption - acoustic consultant - acoustic design - architectural acoustic design

Suspended acoustic rafts – Sound absorption of the edges

The edges of the rafts also absorb sound.

So a couple of large acoustic rafts absorb a little bit less sound than a few smaller acoustic rafts (with the same amount of absorptive materials).

 

Sound absorption of raft edges

sound absorptive edges - Suspended acoustic rafts - sound absorption - acoustic absorption - acoustic consultant - acoustic design - architectural acoustic design

Suspended acoustic rafts – Examples of sound absorption performances

To illustrate this, the graphs below shows examples of sound absorption performance for various raft systems.

 

Note: for rafts, the sound absorption performance is qualified in terms of equivalent absorption area per unit. Not in terms of sound absorption coefficient per m² of material.

 

Equivalent absorption area (m²) of 1200mm x 1200mm acoustic rafts located at different distances from the hard surface above 200 mm, 400 mm and 1000 mm and spaced 500 mm apart (Courtesy of Ecophon)

Equivalent absorption area (m²) of 1200mm x 1200mm acoustic rafts located at different distances from the hard surface above 200 mm, 400 mm and 1000 mm and spaced 500 mm apart (Courtesy of Ecophon) - sound absorptive edges - Suspended acoustic rafts - sound absorption - acoustic absorption - acoustic consultant - acoustic design - architectural acoustic design

 
 
Sound absorption per m² of raft based on rafts of different sizes hung at 1000mm from the hard surface above
(Courtesy of Ecophon)

Sound absorption per m² of raft based on rafts of different sizes hung at 1000mm from the hard surface above (Courtesy of Ecophon) - sound absorptive edges - Suspended acoustic rafts - sound absorption - acoustic absorption - acoustic consultant - acoustic design - architectural acoustic design

 

Suspended acoustic rafts – Specification

Based on the above, you can now understand that the sound absorption characteristics of raft systems don’t just depend on the material of the rafts.

Therefore, in the acoustic specifications, it is important to include the following information:

  • the sound absorption of the material installed in a room (when measured in line with ISO 354:2003 Acoustics — Measurement of sound absorption in a reverberation room)
  • the size of the rafts
  • the spacing between the rafts
  • the distance between the rafts and the hard surface above.

 

Note: the above is applicable to any other free hanging suspended acoustic system.

 

Materials used for suspended acoustic rafts

The materials preferred for acoustic rafts are usually thick fibrous or porous sound absorptive materials such as:

  • fibre glass
  • mineral wool
  • wood wool and mineral wool on top
  • polyester fibres
  • wood fibres

Sometimes, the sound absorptive material is wrapped in a fibrous fabric or even painted.

 

Examples of suspended acoustic rafts

To find examples of suspended acoustic raft products, visit the Acoustic Design Catalogue here.

 

Acoustic plaster systems explained

Have you ever wondered what acoustic plaster systems are?

This post explains:

  • What are acoustic plaster sytems?
  • Advantages and uses of acoustic plaster systems
  • Configurations and characteristics of acoustic plaster systems
  • Sound absorption / acoustic absorption of acoustic plaster systems
  • Sustainability of acoustic plaster systems
  • Installation and workmanship for acoustic plaster systems
  • Examples of acoustic plaster products available on the market

 

Note: Although acoustic plaster systems do look really good, they might not be the solution if you are on a tight budget. Some of the reasons are because they include some high-end materials and have to be installed by specialists.

 

 

What are acoustic plaster systems?

Acoustic plaster systems are sound absorbing systems that are made of fibrous and porous materials to help reduce sound reverberation within spaces.

 

Advantages and uses of acoustic plaster systems

Acoustic plaster systems are usually installed on the ceilings, the soffits and sometimes the walls.

Their advantages are:

  • they have a seamless and smooth appearance.
  • they can be curved or shaped to follow a custom design.
  • they can sometimes integrate heating and cooling systems.
  • although white is preferred most of the time, they can be tinted or painted (with approved paint) in different colors.

Acoustic plasters are generally fire-resistant and can be made moisture resistant.

Lighting systems, sprinklers and audio systems can also be integrated.

Slide the images in the gallery below to see what acoustic pasters look like. To find examples of acoustic plaster products, visit the Acoustic Design Catalogue here.

 

Configurations and characteristics of acoustic plaster systems

Acoustic plaster systems usually come in pre-made panels that require final finishing on site.

They usually include the following:

  • a thick sound absorptive backing layer made of mineral wool, glass fibre, natural fibre or foam.
  • a porous (acoustically transparent) and more rigid base layer.
  • a thin finish layer of plaster trowel or spray applied to the backing layer.
  • a second thin layer can be applied to provide a finer finish.

The thickness of the panels ranges from approximately 10mm to 70 mm.

They can either be fixed to a hard surface or as part of a suspended ceiling (in which case, the thickness of the whole system can reach approximately 220 mm).

Acoustic plaster configuration - suspended ceiling - backing sound absorptive layer - base layer - plaster finish layer - second plaster finish layer - hard surface
Acoustic plaster configuration

 

 

Sound absorption / acoustic absorption of acoustic plaster systems

The sound absorption performance of acoustic plasters depends on:

  • the material of the backing layer.
  • the thickness of the backing layer.
  • the porosity of the surface finishes.
  • if fixed to a suspended ceiling, the depth of the ceiling cavity.

The sound absorption characteristics of acoustic plasters are considered for each square meter of material and can achieve a large variety of performances ranging from Class D to Class A

 

Note: The sound absorption characteristics of acoustic plasters increase with the thickness of the panels, the size of the cavity behind the panels and the presence of a backing layer behind the panels.

 

As mentioned above, plasters can also be painted provided the paint is approved by the manufacturer. This is because paint can modify the porosity of the finish layer and change the sound absorption capacity of the system.

 

Sustainability of acoustic plaster systems

Some plaster systems use natural or recycled materials (such as recycled glass granulate) for the backing layer.

The plaster finish can be made from cellulose, glass or marble granular aggregate, which is a secondary material obtained from the production of natural stone.

 

Installation and workmanship for acoustic plaster systems

Installing acoustic plaster systems requires a high level of workmanship to obtain the sound absorption performance desired and avoid cracks appearing with time.

Suppliers either have in-house and trained installers or certified installers.

 

Examples of acoustic plaster products

To find examples of suitable acoustic plaster products, visit the Acoustic Design Catalogue here.

 

music rehearsal hall - music rehearsal room - orchestra - natural light - acoustics - public performance - acoustic - acoustic consulting - acoustic consultant - performing arts - theatre consulting - acoustic design - architectural acoustic design

 

Design of music rehearsal rooms – Part 3: Other general considerations for rehearsal rooms

Part 1 was going through the aspects that would make successful the acoustic design of music rehearsal rooms.

Part 2 dived deeper into acoustic design with some tips for the planning of such spaces.

Part 3 here goes through other general considerations for rehearsal rooms, including:

  • answering the needs of the main performance space (within large facilities)
  • facilitating access to new audiences
  • providing comfort for the musicians
  • turning rehearsal rooms into performance spaces
  • access and practicalities

It was written by Duck Sceno (Theatre Consultants) with some contributions from Atelier Crescendo. 

Answering the needs of the main performance space

Each type of performance venue has specific needs for the rehearsals.

  • Theatres and Opera houses need a room close to the dimensions of the main stage, with the possibility of installing pieces of set and creating similar light and sound.
  • As well as requiring piano rooms for soloists, Opera houses also need large rooms for choirs and orchestra.
  • Concert halls and Philharmonies need an (or multiple) orchestral rehearsal room(s) able to accommodate a symphony orchestra with optimal acoustic conditions.

Atelier Crescendo’s comment: If the rehearsal room is part of a larger facility, it might be wise to locate it away from other sensitive and/or noisy areas (such as other rehearsal rooms, performance spaces, recording rooms, music practice rooms, etc). This way, you minimise the acoustic interferences between the spaces when they are used simultaneously

 

Rehearsal halls and control room

 

 

Of all the performances, opera and symphonic music are those that remain the most traditional because they are linked to a majority of old musical works, with an audience made of specialist who does not always want to make this art accessible.

Operas can be more accessible because they follow the codes of theatres, that are more democratised, with the spectators facing the stage. People can be more or less seduced by the show. However, they can listen to the music, see the acting and can even sleep (!!) because no one is looking in their direction.

Symphonic music is in itself more difficult to access. The orchestra is the only visual show. There are no sets, no costumes, and the audience surrounds the performers. This allows anyone to watch the yawning and sleepy novices and any other attitudes that would not be appropriate.

 

The rehearsal room can facilitate access to new audiences

High urban densities of large cities have forced the construction of new performance venues outside of the city centres and far from their historical audience.

Between the venue and its adopted neighborhood, the rehearsal rooms are becoming places to gather and exchange where local amateur orchestras and younger musicians can play.

It is also an opportunity to open the building to a new audience and create links with it .

The rehearsal rooms should therefore be made very accessible on the ground floor at lobby level.

 

Providing comfort to the musicians

Transparent, windows and/or glazed façades bring natural light and therefore extra comfort to the professional musicians for whom the rehearsal rooms are actual working places. They also allow the public to see what happens inside.

music rehearsal hall - music rehearsal room - orchestra - natural light - acoustics - public performance - acoustic - acoustic consulting - acoustic consultant - performing arts - theatre consulting - acoustic design - architectural acoustic design
Rehearsal hall – Provision of natural light

When professional musicians are not rehearsing, these rooms can turn into incubators for young future talents who will come to practice together.

 

Turning rehearsal rooms into performance spaces

Rehearsal rooms must be able to transform into small / informal performance spaces.

Rehearsal hall – Piano and small orchestra

Rehearsal hall – Public performance and grand orchestra

 

They need to be able accommodate unexperienced audiences installed in a frontal configuration, with a clear separation between the stage and the audience, to focus more on music and its feelings.

Concequently, the rooms need to achieve scenographic, acoustic and safety requirements. It will be necessary to design and study the installation and the sightline of the audience, the concealment and the control of the natural light with curtains and lightlock accesses.

Atelier Crescendo’s comment: the acoustic contribution of the seats will also need to be considered. 

Rehearsal hall – Provision of retractable seating

 

 

A control room, part of the technical infrastructures, might be useful with open access to promote creativity and inspire future performances.

The acoustics will have to be variable according to the use of the room (it is for a rehearsal or a show? with or without an audience? with a small or a large orchestra? with amplified or purely acoustic music?).

Atelier Crescendo’s comment: This can be done with “passive” variable acoustic systems. Read Variable sound absorption systems for more information. It is also possible to use “active” variable acoustic systems with electro-acoustic systems (using microphones, loudspeakers and special audio processing devices).

Rehearsal hall – Control room

 

Access and practicalities

Like any space open to the public, it will be necessary to study the number and the dimensions of the accesses and the circulations.

The installation conditions for the public with emergency lighting and signage, and taking into account all the publics including people with reduced mobility.

 

The function of the rehearsal rooms is important. Their technical aspect is even greater as their “small” size requires optimisations. Their need for a high flexibility requires specific studies and mixed infrastructures. Rehearsal rooms are not always considered at their fair value in briefs / programs and budgets, in France and on international projects.

 

 

Design of music rehearsal rooms – Part 2: Some acoustic design tips for music rehearsal rooms

Part 1 was explaining what makes a successful acoustic design for music rehearsal rooms.

Part 2 here dives deeper into acoustic design by giving you a few tips for the planning of such spaces. It covers the following topics:

At the end of this part, you will also find all the documents and the materials reviewed to help writing the articles. 

Part 3, written by Ducks Sceno (Theatre Consultants) with contributions from Atelier Crescendo, highlights other general design considerations you should think about for rehearsal rooms.

Enjoy the read.

 

Sound reverberation conditions for music rehearsal rooms

Good sound reverberation conditions in a large music rehearsal rooms contribute to: 

  • the audibility and the clarity of the musical messages
  • the musical intonations
  • the musical tones 
  • the articulations
  • the balance of the sounds

Therefore, unsurprisingly, getting the reverberation conditions right is THE focus point for the acoustic design.

You need to consider:

  • the overall sound reverberation quality of the rehearsal room to control the loudness and the clarity of the music played. You usually do this by adjusting the volume and the general amount of sound absorptive/reflective materials.

 

Note: read Sound reverberation – Part 1: Basics if you need a refresher about sound reverberation and reverberation time. 

 

  • the timing of the sound reflected back to the musicians (Do you remember? Part 1: The goals for a successful acoustic design explains the necessity to balance early and late reflected sound for musicians on stage). You manage this by adjusting the orientation and/or the shapes of the surfaces around the musicians and the orchestra conductor. Sometimes, you also need to add surfaces such as overhead reflectors, orchestra shells, etc. 

 

reflected sound energy - sound reflections -- stage acoustics - direct sound - early reverberation - late reverberation - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

  • the frequency content of the sound reflected back to the musicians (Do you remember? the end of Part 1: The goals for a successful acoustic design explains that musicians like to hear rythms and musical expressions that are mostly emitted at medium and high frequencies). Therefore, the reflected sound should contain less energy at low frequencies than at higher frequencies. You manage this by adjusting the dimensions and physical properties of the finishes and the materials (ex: thickness, width, length, density or also stiffness) around the musicians, so that they absorb more energy at low frequencies. 

reflected sound energy around the musicians - low frequencies - - stage acoustics - medium 'mid' frequencies - hiigh frequencies - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

 

 

Volume and space for music rehearsal rooms

Part 1: The goals for a successful acoustic design explains that containing the sound energy of the music is key to ensure a successful rehearsal room.

For large ensembles (including 20 musicians), the room volume should to be relatively large so that the music doesn’t sound too loud. If the ensembles include loud instruments (such as brass instruments or also percussions), the volume should be even larger

You shoud also set an area where artists will sit (or stand!) and make sure they are not too close to (vertical and flat) acoustically reflective surfaces like the walls. 

Norwegian Standard 8178:2014  – Acoustic criteria for rooms and spaces for music rehearsal and performance  provides guidance on the necessary volume and space  for music rehearsal and perforance spaces depending on the type of music played inside. Read Acoustic design planning for music spaces  for more details. 

 

Note: The international standard ISO 23591:2021 – Acoustic quality criteria for music rehearsal rooms and spaces provides the same guidance.

 

For large music ensemble rooms with more than 20-25 musicians (our case here), you should consider the dimensions below.

Volume and space - stage acoustics -- ISO 23591:2021 - Acoustic quality criteria for music rehearsal rooms and spaces - Norwegian Standard 8178:2014  - Acoustic criteria for rooms and spaces for music rehearsal and performance - room height - net volume - net area - performers - room proportions and geometry - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

QUIET MUSIC

(just string instruments, choirs, etc)

 

Net volume

minimum 700 m3

 

 

 

 

Net floor area

minimum 50 m2

+

minimum 2 m2 /musician

 

Soffit / Ceiling height

minimum 5 m

LOUD MUSIC

(i.e. brass bands, concert bands, big bands,

percussion ensembles, symphony orchestras)

Net volume

minimum 30 m3 / musician

concert bands: minimum 1000 m3

brass bands: minimum 1500 m3

Symphony orchestras: minimum 1800 m3

 

Net floor area

minimum 120 m2

+

minimum 2 m2 /musician

 

Soffit / Ceiling height

minimum 5 m

 

 

Room proportions and geometry for music rehearsal rooms

One of the most successful shapes for large music ensemble rooms is the cuboïd shape such as a cube or the so called ‘shoebox’ shape. 

  What is a room with a shoebox shape? It is a room with a rectangular floor area, parallel side walls and tall ceiling / soffit. The base volume is two cubes located next to one another.

Room proportions and geometry - shoebox shape - cube - squares - stage acoustics -- acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

However, sound diffusive finishes and/or shapes should be planned to avoid creating flutter echoes.

You should also avoid any shapes that focus the sound in certain areas. This is because the sound field should be as ‘diffuse’ as possible in the room.

 

Note: you obtain a diffuse sound field in a space when the sound pressure level is uniform throughout the space. 

 

Examples of shapes that focus sound are presented below.

avoid

Concave shapes

 

Dome

Dome - concave shapes - shapes to avoid - Room proportions and geometry -- stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

Curved wall 

curved wall - shapes to avoid - Room proportions and geometry - stage acoustics -- acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

Avoid

pitched/slanted Shapes

 

Pitched ceiling

- stage acoustics -slanted roof - slanted ceiling - slanted soffit - pitched roof - pitched ceiling - pitched soffit - shapes to avoid - Room proportions and geometry - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

Angled walls

angled walls - shapes to avoid - Room proportions and geometry -- stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

 

Acoustic treatment for music rehearsal rooms

For large music rehearsal rooms, it is very likely that most walls need to include some acoustic treatment (or at least acoustic consideration) in the form of sound absorption or sound diffusion.

The function of the acoustic treatment varies depending on:

  • the location of the walls in relation to the orchestra
  • the height of the wall section considered.

Therefore, this section presents acoustic design tips for :

  • the wall behind the conductor
  • the walls at low level
  • the walls at upper level

Acoustic treatment for the walls of music rehearsal rooms

Wall behind the orchestra conductor

The wall behind the orchestra conductor should include some amount of sound absorption and/or diffusion.

This avoids strong ‘specular’ reflections to hit the wall and reach the conductor again, creating the perception of a virtual orchestra behind her/him (see below, specular and diffusive reflections are explained).

flat and solid wall acoustically reflective behind the conductor - virtual orchestra perceptible - stage acoustics -- acoustic treatment for the walls - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

acoustically absorptive wall behind the conductor -- stage acoustics - virtual orchestra less perceptible or imperceptible - acoustic treatment for the walls - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

irregular wall acoustically diffusive behind the conductor - - stage acoustics - virtual orchestra less perceptible or imperceptible - acoustic treatment for the walls - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

Note: what is a specular reflection? a specular reflection is, similarly to light reflected on a mirror, a reflection that bounces off a surface with the same angle as when it hits the surface. A diffusive reflection is a reflection that bounces off a surface in different directions

 

 

angle of incidence - angle of reflection - incident wave - stage acoustics -- reflected wave - specular reflection - diffusive reflection - virtual orchestra less perceptible or imperceptible - acoustic treatment for the walls - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

Walls at low level

Assuming most musicians face the conductor, you should avoid sound absorbing finishes at low level, i.e. approximately below head height. Instead, you should favor elements that reflect and diffuse sound at medium and high frequencies

This ensures that the conductor and the orchestra receive lateral sound reflections (musicians rely more on lateral reflections to hear themselves and others).

sound diffusive lower side walls - lower walls - acoustic treatment for the walls - - stage acoustics -acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

However, there could be an option for these surfaces to absorb some amount of acoustic energy at low frequencies.

For this applications, materials that can absorb sound at low frequencies generally include:

  • a sheet / board /face that is not so dense 
  • a cavity behind with sound absorption inside as an option.

Examples of such materials are:

  • plasterboard or gypsum based boards on frame
  • timber sheets/boards mounted on frame
  • suspended ceilings

 

Note: There are many other specialist materials and configurations that can absorb sound at low frequencies.

 

On the walls located far from the musicians, it might be necessary to install sound absorbing finishes to avoid any late (or unwanted) reflected sound.

 

Walls at upper level

The upper walls, i.e. approximately above head height, can include sound diffusive surfaces.

However, they are a good location to add broadband absorption materials to lower the overall sound reverberation within the rehearsal room.

 

What are broadband absorption materials? they are materials that absorb sound over a large range of frequencies. Examples of such materials are fibre, wool or also foam based materials.  

 

sound diffusive upper side walls - sound absorptive upper side walls - upper walls - - stage acoustics - acoustic treatment for the walls - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

Acoustic treatment for the ceiling / soffit of music rehearsal rooms

A fully or partially sound absorptive ceiling can also be useful to reduce the overall sound reverberation within the rehearsal room. Especially when you need to absorb sound at low frequencies

 sound absorptive ceiling with cavity (optional) - acoustic treatment for the ceiling soffit - - stage acoustics -acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

Acoustic consideration for the floor of music rehearsal rooms

Hard floor finish fixed on concrete hardly absorbs any sound. 

However, a raised hard floor finish can absorb sound at some low frequencies due to the cavity created by the system.

This feature can be particularly useful for the musicians who rely on reflected sound at medium and high frequencies (as mentionned previously). 

For the same reason, carpet should be avoided as it absorbs sound at medium and high frequencies.

See below some ideas of sound absorption performances achieved by different floor finishes. 

 

Sound absorption coefficients of different floor finishes
(ref: Acoustic Absorbers and Diffusers, Theory, Design and Application – Third Edition – Trevor J. Cox and Peter D’Antonio)

 

 

 

 

Overhead reflectors for music rehearsal rooms

For large and tall spaces where large orchestras play, it might be necessary to plan for sound reflectors above the musicians, also called ‘overhead reflectors’

They are useful to provide additional early reflections and improve the acoustic conditions within the orchestra. Sometimes, additional wall reflectors above head height or even orchestra shells are also installed to provide the same effect.

For large (and loud) ensembles, overhear reflectors should be at approximately 8-10 m above the floor level.

For small (and quiet) ensembles, they could be located as low as 6 m above the floor level . 

 

If the overhead reflectors are too low, they could cause some loudness issues (i.e. the music will sound too loud)

 

You should favor arrays of smaller reflectors, instead of a single large reflector or just a few large reflectors, to optimise the diffusion of the acoustic energy across the orchestra. 

Some of the most common shapes for overhead reflectors are curved (convex), random waves, ‘QRD’ type (‘QRD’ stands for Quadratic Residue Diffuser) or any other shapes with irregular and random width and depth.

Flat reflectors should also be avoided.

See below some examples of acoustic diffusers (although many other types of diffusers exist). 

single reflector - single curved reflector - overhead reflectors - overhead diffusers - stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

array of reflectors - overhead reflectors - overhead diffusers - stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

array of profiled reflectors - overhead reflectors - overhead diffusers - stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

 curved reflectors - overhead reflectors - overhead diffusers - stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

round mushroom reflectors - overhead reflectors - overhead diffusers - stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

3D QRD diffusers - 3D QRD reflectors - overhead reflectors - overhead diffusers - stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 random wave diffusers - random wave reflectors - overhead reflectors - overhead diffusers - stage acoustics - acoustic design for music rehearsal rooms for orchestras - large music ensemble rooms - sound reverberation - room acoustics

 

You should favour relatively dense and stiff materials to ensure that sound hitting the reflector is not absorbed, especially at the lower frequencies due to the resonance of the reflectors.

Examples of materials are:

  • gypsum based
  • dense plaster
  • wood particle or fibre based
  • glass

Did you know? even with a dense and stiff material, a flat reflector can resonate and absorb sound at low frequencies. Curving it will stiffen it, increase its natural frequency and reduce the low frequency absorption. 

 

 

 

Background noise levels in music rehearsal rooms

A music rehearsal room is an environment where the musicians need to hear their own musical details and those of the other musicians. 

Because a high background noise can mask these details, it is important to keep it as low as possible when the space is in use. 

Sometimes, music rehearsal rooms are also used as large recording studios for large ensembles and orchestras. So it is important to ensure acoustic conditions suitable for recording activites, i.e. with a very low background noise levels.

Therefore, the acoustic design should include control of noise from (some of or all) the following sources:

  • ventilation systems
  • mechanical systems and machineries
  • electrical systems
  • external noise (such as road, air or even rail traffic)

 

References for acoustic design of music rehearsal rooms

The following documents and materials have been reviewed to write this article and Part 1: The goals for a successful acoustic design .

  • J. Meyer – Some problems of opera house acoustics – Proceedings – Symposium on acoustics and theatre planning for the performing arts (1986)
  • P. Adams – Acoustic design of large rehearsal spaces – Proceedings – ISRA (2019)
  • A. Gade – Investigation of musicians’ room acoustic conditions in concert halls, Part I: Field experiments and synthesis of results – Acustica (1989)
  • A. Gade – Investigation of musicians’ room acoustic conditions in concert halls, Part II: Methods and laboratory experiments – Act Acustica United & Acustica (1989)
  • International Standard Organisation – “ISO 3382-1 – acoustics measurement of room acoustic parameters – Part 1: Performance spaces” (2009)
  • R. Wenmaekers – How orchestra members influence stage acoustic parameters on five different concert hall stages and orchestra pits – Journal of the Acoustical Society of America ‘JASA’ (2016)
  • J Dammerud – Attenuation of direct sound and the contributions of early reflections within symphony orchestras – ournal of the Acoustical Society of America ‘JASA’ (2010)
  • L. Panton – Investigating auditorium acoustics from the perspective of musicians – PhD  thesis – University of Tasmania (2017)
  • European Parliament and Council, Directive 2003/10/EC on the minimum health and safety requirements regarding the exposure of workers to the risks arasing from physical agents (noise) (2003)
  • Sound Advice: Control of noise at Work in music and entertainment – the Health and Safety Executive (2008)
  • E. Hatlevik – Are musicians affected by room acoustics in rehearsal rooms – Master’s Thesis – Norwegian University of Science and Technology NTNU (2012)
  • O. Riduan – Designing small music practice rooms for sound quality – Proceedings – International Congress on Acoustics (2010)
  • C. Pop – Music practice rooms: Ambitions, limitations and practical acoustic design – Proceedings – International Symposium on Music Acoustics (2019)
  • H. Drotleff – New room acoustic design concept for rehearsal rooms – CFA DAGA ’04 , Strasbourg 22-25/03/2004 (2004)
  • H. Koskinen – Facilities for music education and their acoustical design – article – International Journal of Occupational Safety and Ergonomics
  • McCue – Rehearsal room Acoustics, acoustical design of music education facilities – Journal of Acoustical Society of America (1990)
  • Lamberty – Music Practice Rooms – Journal of Sound and Vibration (Vol. 60, No.1)
  • R. Walker – Acoustic Criteria and Specification – BB R&D White paper WHP021 (2002)
  • Skalevik – Rehearsal room acoustics for the orchestra musician – Proceedings – Baltic-Nordic Acoustics Meeting (2014)
  • O’Brien et al. – Nature of orchestral noise – Journal of Acoustic Society of America (2008)
  • G. Leitermann – Theatre Planning – A focal press book (2017)
  • J. Strong – Theatre Buildings – A design guide – Association of british theatre technicians (2010)
  • Norwegian Standard NS 8178:2014 – Acoustic criteria for rooms and spaces for music rehearsal and performance
  • R. Wenmaekers – Stage acoustics sound exposure – www.stageacoustics.wordpress.com/sound-exposure-reduction

Design of music rehearsal rooms – Part 1: The goals for a successful acoustic design

 

When Atelier Crescendo asked Sir James MacMillan about how the quality of the music spaces can contribute to the musical creativity, the music education and the music performance during his interview, he replied:

“It is very important for young musicians to sound good in the early stages of their musical development. If they sound good on their instrument, in their voice, in their choir, in their ensemble, to their peers, to their parents and to the local audience that comes to listen, then the delight of music-making is enhanced. And that delight is part of what motivates a young musician to continue.

So, it is vitally important to get the acoustical design right in an educational setting.”

Sir James MacMillan

Following this comment, it was hard to not write anything about the acoustic design of music rehearsal rooms.  

But the design of such spaces goes beyond the acoustic aspect. So, based on their experience and knowledge, Atelier Crescendo and Ducks Sceno have collaborated on writing a series articles to raise insight on what the design of rehearsal rooms should consider. 

The topic is pretty large for acoustics as there are different types of rehearsal/practice rooms to cover.

Therefore, this series of articles only consider rehearsal spaces for orchestras or ensembles of a ‘standard’ size

 

  what is considered an orchestra/ensemble of a ‘standard’ size? this is a group of musicians that includes:

  • between 12 and 35 musicians.

  • a minimum number or no power amplified instruments.

 

Also, some acoustic aspects have not been treated in this series. They are external noise intrusion, the internal sound insulation, noise and vibration from the building services. If you need some insights about these topics, you can read the following posts:

The first article of the series answers the question What are the goals for a successful acoustic design?

Part 2 provides some acoustic design tips when planning the design of rehearsal spaces. 

Part 3,  written by Ducks Sceno (Theatre Consultants) with contributions from Atelier Crescendo, highlights other general design considerations you should think about for rehearsal rooms

 

What is a successful acoustic design for a music rehearsal room? 

 

successful acoustic design for rehearsal rooms - rehearsal room - musical acoustical acoustics - architectural acoustics - architectural design - performing arts - sound reflection - sound absorption - sound diffusion - acoustic consultant - acoustic engineer - concert halls acoustics - theatre acoustics

You can consider successful the acoustic design of a rehearsal room when you have created a space:

 

  • where musicians can hear themselves and each other.
  • where the music energy is contained to the right level (not too loud but not too quiet either).
  • where musicians enjoy playing and they can prepare them well to perform (this is when the rehearsal space is part of a large performance facility with a main – larger – venue). 

These three aspects are discussed below in more detail.

 

 

A space where musicians can hear themselves and each other 

hearing instruments - hearing the music - successful acoustic design for rehearsal rooms - rehearsal room - musical acoustical acoustics - architectural acoustics - architectural design - performing arts - sound reflection - sound absorption - sound diffusion - acoustic consultant - acoustic engineer - concert halls acoustics - theatre acoustics

Obviously, to hear your own instrument and other instruments, there needs to be a balance between the volume of every instrument. 

To hear your own instrument, its volume needs to be higher (to your ears!) than the volume of the music around you. But not too high either, because you still want to hear the other instruments to play in sync with them.

Also, a good balance would make the quieter or more remote instruments still audible. Whilst the louder and close instruments are attenuated enough, so that their sound doesn’t mask the others. 

 

Note: We are talking about instruments here, but the same applies to voices.

 

But, in an environment with reflective surfaces surrounding you, it’s not just about volume. It is also about the timing!

More exactly, when the sound of your and other instruments, reflected on the surrounding surfaces,  reaches you.  

This is when you get into the science of sound reverberation.

 

Note: if you need a refresher about the basics of sound reverberation, you can read these two posts:

 

When designing an environment for orchestras and ensembles, you need to balance the following:

  • the direct and reflected sound energy of the instruments arriving early to your ears, and ;
  • the reflected sound energy of the instruments arriving late to your ears.   

Generally, the reflected sound energy arriving within the first 100 ms is quite beneficial for the intelligibility and clarity of the musical messages.

 

hearing instruments - hearing the music - successful acoustic design for rehearsal rooms - rehearsal room - musical acoustical acoustics - architectural acoustics - architectural design - performing arts - sound reflection - sound absorption - sound diffusion - acoustic consultant - acoustic engineer - concert halls acoustics - theatre acoustics
Example of sound reverberation in a rehearsal room

Finally, it is particularly important for the musicians to hear musical details such as attack transients. They allow to communicate the rhythm or the musical expressions and are generally emitted at mid and high frequencies.

So it is crucial to keep the direct and reflected sounds at these frequencies as much as possible and absorb some amount of low frequencies.

 

 

A space that contains music energy to the right level containing music sound - successful acoustic design for rehearsal rooms - rehearsal room - musical acoustical acoustics - architectural acoustics - architectural design - performing arts - sound reflection - sound absorption - sound diffusion - acoustic consultant - acoustic engineer - concert halls acoustics - theatre acoustics

Obviously, playing within an orchestra that sounds loud is not comfortable. But the main problem is that it causes hearing loss if it happens regularly

Most of the time, musicians can’t wear ear defenders or ear plugs because they need to be able to hear themselves as well as their fellow musicians. 

An orchestra can sound loud for several reasons:

  • the rehearsal space is just too small for an orchestra.
  • the rehearsal space is too small for the type of orchestra. In other words, there are too many loud instruments (such as percussions, brass instruments, amplified instruments, etc) and the volume of the space is not big enough to accommodate them.
  • some surrounding surfaces reflect too much sound at certain locations. 
  • some hard surfaces are too close. These can be the walls, the balconies or also the overhead reflector(s).  
  • there are too many hard finishes (i.e. sound reflective) and not enough sound absorptive materials.

All or some of the above can lead to a form of Lombart effect (also called cocktail effect). The orchestra is too loud for the musicians to hear themselves. So they play louder. But their neighbours also play louder. And that snowballs throughout the orchestra making it very loud

 

A space where musicians enjoy playing and can prepare them well to perform

musicians enjoying playing music and rehearsing - successful acoustic design for rehearsal rooms - rehearsal room - musical acoustical acoustics - architectural acoustics - architectural design - performing arts - sound reflection - sound absorption - sound diffusion - acoustic consultant - acoustic engineer - concert halls acoustics - theatre acoustics

Sometimes the rehearsal space is part of a large performing arts facility. It can then be used by either the local orchestra or touring orchestras who need to do their final adjustments before the ‘big concert’.

 

  Note: Sometimes, rehearsal spaces are also used as actual performance spaces for smaller audiences.

 

Because every performance venue is acoustically different (this is what makes them unique!), musicians always have to adapt the way they play for the space. Whilst the main performance space might not always be available, the rehearsal should offer an opportunity to know what it is like to play on stage. 

Obviously, this is to a certain degree, because you can’t replicate the exact same acoustic conditions of the stage. At least, musicians should be given a taste.  

 

On a more general point of view, rehearsal spaces should make the musicians ‘feel at home’ as much as possible, whether they are from the local orchestra or a touring orchestra.

It should be a comfortable place (acoustically, visually and physically) where musicians enjoy playing and practicing. So that they are in the best conditions to communicate the emotions of their music. 

So the architectural design should be carefully thought out including:

  • the shape of the finishes and the room itself.
  • the color of the finishes and the furniture within the room.
  • the layout of the room and of the building.
  • the acoustic and the physical flexibility of the room.
  • the access to the rehearsal room from other spaces of the building (such as changing rooms, restaurant, reception, toilets, breakout areas, etc) 

 

References for acoustic design of music rehearsal rooms

The documents and materials reviewed to write this article are presented at the end of Part 2.

 

Variable sound absorption systems

 

 

 

If you are working on a building project with a large space, you might want to use it for a broad range of activities.

Depending on the building is, the activities could be:

  • amplified music performances
  • quiet acoustic music performances
  • loud acoustic music performances
  • drama performances
  • conferences or lectures
  • sports events
  • exams
  • fairs
  • and more.

The space will not only need to be very flexible physically to accommodate these activities, but also acoustically. In fact, each activity requires very different sound reverberation conditions to work optimally and ensure acoustic comfort for the users (and listeners for some cases).

 

Note: If you need a refresher on the basics of sound reverberation, go to this page.

 

One of the ways to make a space acoustically flexible is by changing the sound absorption in the space. Essentially, you either:

  • reveal or add sound absorptive materials to make the room less reverberant, and;
  • hide or take away sound absorptive materials to make the room more reverberant (or more lively).

This is done with systems called variable acoustic systems or also variable sound absorption systems.

 

  Note: Other ways of changing the sound reverberation in spaces is by changing their volume or artificially adding reverberation with electroacoustic systems.

What are these systems? This post presents, with pros and cons explained, some of the most commonly used variable sound absorption systems, including:

 

Note: the following documents have been helpful to write this post:

  • Auditorium Acoustics and Architectural Design – Mike Barron;

  • Acoustic Absorbers and Diffusers: Theory, Design and Application (Third Edition) – Trevor Cox and Peter d’Antonio

  • Sound Materials: A Compendium of Sound Absorbing Materials for Architecture and Design – Tyler Adams

Are you looking to understand how acoustic products work and find examples available on the market? 

Visit the Acoustic Design Catalogue by following the link below.

 

Acoustic Curtains/Drapes


Acoustic curtains can be either:

  • extended along walls to lower the sound reverberation in a space, or;
  • stored in corners or in dedicated cupboards to increase the sound reverberation.

To know more on acoustic curtains (such as installation, acoustic performance, characteristics of the fabric, etc), follow this link to the Acoustic Design Catalogue.

Variable sound absorption with curtains (left: extended - right: stored) - variable acoustics - acoustic curtains - acoustic drapes - performing arts
Variable sound absorption with curtains (left: extended – right: stored)

 

Pros

 

Acoustic curtains drapes - relatively cheap  Relatively cheap

Acoustic curtain systems mostly involve fabric and a rail, which is relatively inexpensive compared to other sound absorption materials or systems.

 

acoustic curtains drapes - easy to deploy   

Easy to operate

They are also manually operated. No need for a complicated motorised system.

 

    Quick to deploy

Unlike certain systems that take a few minutes to deploy (or even longer), deploying acoustic curtains only takes a few seconds.

 Cons

 

Acoustic curtains - fullness - sound absorption limited  Limited sound absorption

Curtains are not the most efficient sound absorber. Consequently, you need more material to cover large wall surfaces and provide a sufficient variation in the reverberation time. If you design a space with a large volume, you could also struggle to find enough available space.

 

Absorb sound at mid and high frequencies - sound absorption  Absorb sound at mid and high frequencies

As a fibrous material, fabric is more efficient at absorbing sound at mid and high frequencies than at low frequencies.

Therefore, you will need to find other sound absorption means if you want to control the sound reverberation at low frequencies (especially in spaces where music is played). 

Jonathan Berman - Peter Serkin - Tanglewood

 

Interview with Jonathan Berman – Part 2: Sounds and acoustics

 

 

 

 

MF: Do you also work on the positioning of the instruments depending on the hall?

JB: Absolutely – for me it’s an incredibly important aspect, not just for the quality of sound and comfort of playing but also as a means of expression. Orchestras have, throughout the ages, been set up in many different ways, depending on the repertoire, the time period, the concert hall and for me it is definitely part of the expressive role of a conductor to be flexible with orchestral seating.

Just to begin with, there are many pieces (particularly written in the last 60 years or so) where the composer asks for specific or unusual seating plans of orchestras because the roles played by certain instruments or groups of instruments do not function in the traditional manner.

The most famous extreme example of this would be Stockhausen’ Gruppen where he asks for three separate orchestras to surround the audience creating the most astonishing surround sound effects.

Stockhausen Gruppen - Jonathan Berman
Stockhausen Gruppen with three orchestras surrounding the audience

But there are many examples of pieces placed on stage with different layouts. From Stockhausen’s Fünf weitere Sternzeichen where the strings are placed behind the winds, brasses, harps and percussion and space is left between the conductor and the audience for a solo tuba to move around. Or Boulez’s Rituel where 8 groups of players are asked to be as far away from each other as possible on stage (perhaps an early form of social distancing!).

For more traditional repertoire there are some decisions you have to make, for instance where to place your violins. In most music before around 1825(ish), Beethoven, Mozart and Haydn for example, you probably want the 1st violins on the conductor’s left hand side and the 2nd violins on the right hand side, so that the audience will experience a stereo, antiphonal effect as the composers often write dialogues between the violins into their music. 

Jonathan Berman - Orchestra layout with violins on each side
Orchestra layout with 1st violins on the left side and the 2nd violins on the right side

Whereas for some composers like maybe Mahler, Tchaikovsky, Strauss and some more modern composers, you have all violins sitting on the same side so that the sound image comes from the same place and arrives already mixed to the audience. 

There is also a question in every concert about the double basses. Personally, I love big bass sounds and I want the audience to really hear them as the foundation of the music.

I love having bases along the back of an orchestra, as opposed to one side, so that the sound of the lowest note in the orchestra permeates through the orchestra and the whole sound (and intonation) of the orchestra is based on the bases (pun intended). Although of course, it depends on the acoustic properties of the venue and what sounds best.

However, there is some music for which the music written by the composer demands different orchestral textures and timbres. A great example is Stravinsky’s music for which you would place your bass section to one side so that the bass sonorities are clear and more separated from other instruments in the orchestra to best serve the way the music functions.

And then, of course, the complication is that you are not playing in venues that are all the same or with robots but real people. If you want the music in a certain way for the audience, you need to create conditions for the musicians to play to their best. The setting up of the orchestra also becomes a dialogue between your ideals, the venue and the players.

For the recording of the Symphony No. 1 from Franz Schmidt, I really wanted antiphonal violins, because I love that stereo sound and I felt there were a number of passages in the music where that would really add something. However, when we got into the sessions, the violins didn’t feel comfortable being so far away from each other (in the recording studio they struggled to hear each other from opposite ends of the stage). Because there are many passages with a lot of delicate details that they had to really get together as a singular violin section, the leader advised me to put them all on one side, which I did.

Jonathan berman - Orchestra layout for the recording of the Symphony No. 1 from Franz Schmidt
Orchestra layout for the recording of the Symphony No. 1 from Franz Schmidt

Suddenly they played with such confidence as they could all hear each other that it simply sounded so much better and outweighed my initial ideas. (This also shows the value of listening to what the players have to say – especially when they know their own orchestras and venues much better than you do!)

MF: Part of the design of stages is to control the loudness on stage, so the music is not too loud and you manage the noise exposure of the musicians. What are your views and experience on this?

JB: Well this is a very important issue, particularly at the moment. Modern orchestras accept (and even expect) the wearing of earplugs and sound protectors on stage as a normality. They are necessary to protect musicians who are seriously struggling with hearing loss after years of playing in orchestras – and even more in opera pits.

However, it is undeniable that the volume of orchestras has increased over the years. For a number of reasons – the halls we play in are often much bigger, the instruments have changed as well, all of which has developed symbiotically with a changing aesthetics of orchestral and instrumental sound.

In older halls like the Musikverein, you notice how loud a modern orchestra can sound. Whereas if you play in Chicago Symphony Centre, in The Shed in Tanglewood or the Royal Albert Hall, suddenly you have to develop this sound which projects and travels over huge distances.

The Shed - Tanglewood - Jonathan Berman
The Shed, Tanglewood

For me, I have actually learned a lot from this phenomenon. The orchestras whose sound I love (Vienna Philharmonic, Cleveland Orchestra, the Philadelphia Orchestra, Paris Conservatoire Orchestra, Czech Philharmonic, Concertgebouw Orchestra or Berlin Konzerthaus Orchestra) all play (or played) in smaller, old fashioned halls where making music isn’t about projecting your sound to the back of the 5000 seater hall, but more about creating warmth. Practically you don’t need to play too loudly in order for everyone just to hear, and so what you can do is discover more colours and nuances in the sound colours.

This idea has been central to my ideal of orchestral sound and, whilst both conducting and rehearsing, I often find myself asking orchestras to play softer, focusing on tone quality and warmth more than projection.

MF: What is your view on the quality of different styles of halls? Especially between shoebox and vineyard styles.

Yes, very interesting question. The first thing is that all musics are different. And I don’t just mean classical, pop, etc, I also mean Bach, Mozart, Haydn, Stravinsky, Boulez, etc. There is no absolute ‘perfect’ acoustic where you can play all music equally effectively. So even the idea that one style of hall is better acoustically and the other style better visually is not true (for me) because it depends on the repertoire being performed.

I have to say that I have experienced phenomenal concerts in both styles of hall and enjoyed performing in both, but I think the audience perspective is more important – at least it has to take into account the orchestra’s perspective because they are highly unlikely to perform a great concert if they are not comfortable on stage.

I love the social ideal in a vineyard hall (think Berlin Philharmonie, the New World Centre Miami, or the Leipzig Gewandhaus from the 1980s) that the audience is closer to the stage, they have better visual contact, and the hall doesn’t dissect communities by separating the expensive seats from the cheap seats.

New world symphony - miami
New World Symphony, Miami

However, I sat in many different seats in shoebox concert halls and felt incredibly connected to the stage – particularly when the halls aren’t too big (Concertgebouw, Musikverein, Snape Maltings or Berlin Konzerthaus).

Interesting to note that in the old style halls, the most expensive seats are normally at the front of the balcony which are the furthest from the stage, but of course still close enough to feel very connected.

I do think that we shouldn’t forget that music is an auditory art form. Whilst there are many ways to enjoy concerts, for social reasons, meditating on your day, enjoying the visual drama of the playing of the instruments, or just having a nice nap. But it is when somebody listens to the music actively that a live concert becomes something unique and nothing else in the world comes close. This is the experience we should all be striving for people to have.

MF: Can you share a little more about your favourite venues? There may be some you would advise people to go to or you have some interesting tips about some types of venues.

One of the cleverest halls is the Seiji Ozawa Hall in Tanglewood. It was completed in the 90s and in essence, it is a very traditional and fairly small shoebox with balconies. There is a summer festival there where the Boston Symphony Orchestra goes. The back wall of the hall can be folded out and opens to this sort of amphitheatre of a grass hill where people come, have picnic and listen to music all weekend. It is an amazing place. 

 

Seiji Ozawa Hall - Tanglewood - Jonatha Berman
Seiji Ozawa Hall, Tanglewood

It really has both the inside and the outside atmospheres. You get this wonderful, warm acoustic, and actually, over the six or seven years of conducting concerts there, the increase of moisture in the wood seems to have improved the warmth of the hall.

I think Suntory Hall in Tokyo is one of the most extraordinary halls. There is something magical about the sound there. The sound feels like you are not only close to the stage, but somehow you are also right at the back of the hall.  Music sounds there as one single sound, it has this sort of visceral attack, very clean, very clear. You hear all the details and also the resonance of the space.

Opera houses also are very interesting. They are often quite dry. You have this small box in which the orchestra plays (the orchestra pit), and the sound goes vertically up from this pit, which the audience then hears mostly as reflected sound. You have singers on stage, who sing directly at the audience and the orchestra (allowing both to hear the singers clearly) and for the audience you get a wonderful balance between the reflected orchestral sound and the direct vocal sound. If you go to the Royal Opera House (London) or Palais Garnier (Paris) or even a smaller house like Gyndlebourne or the Comischer Oper (Berlin), the absolute best seats to hear a performance from are right at the very top at the very back (often the cheapest seats), but you will hear the most perfect sound. You hear this sort of shimmering effect, the balanced sound, the voice and the orchestra amplified in its own resonating chamber, as though the pit becomes part of the instrument of the orchestra like the body of a violin or the sound board on a piano. It’s an extraordinary experience.

Actually, almost the worst seats are at the first row of the stalls. At the first row, you are very close to the action visually, but the balance between the direct sound coming from the voice and the sound of the orchestra is unmixed and can sound separated. That’s also why when rehearsing for opera, you have somebody sitting in the front few rows balancing from there – normally if the balance is ok right at the front it will work everywhere else.

MF: For some halls, the acoustic conditions might not always be optimal depending on where you sit. The music you hear on stage could also be very different compared to the music you hear in the rest of the hall. How do you prepare for all this?

There are some concert halls where if you sit in the wrong seat, it might be an expensive seat, but if you sit in the wrong seat, it is really not a good experience. In a really good hall, there are very few differences between the seats.

What happens then is, most of the time, conductors or managers never sit in them. They judge performances from a very specific select set of locations. We forget sometimes that if you sit in a different place, you can hear something different.

An orchestra manager some years ago said to me “Look, you need to sit in every seat”. Because you need to know how every one of your audience feels. He was trying to find solutions to make all his audience happy. If we want to inspire people into music we love and make them hear what we want them to hear, we need to make sure we play well for every single seat.

Practically, to do this as a conductor, you often have somebody assisting you whose job is mostly to walk around the hall and give little notes back about how it sounds in the hall. I also find it hugely useful to have assistants, because they can conduct five minutes whilst you can walk around the hall and listen, so that you can really understand the translation from what it sounds like on the podium to what it sounds like in the hall.

There is another trick that I learned from one of my mentors, a conductor called Stanislav Skrowaczewski. 

Stanislav Skrowaczewski - Jonathan Berman
Stanislav Skrowaczewski

He used to occasionally turn 90 degrees to the orchestra, by putting his left ear towards the empty space, to listen to the hall.

You have to work at it a bit, but it gives you a really good sensation of what the hall sounds like, as opposed to when you are facing the orchestra where you hear mostly the direct sounds from the instruments.

Doing this gives you one more bit of information and it allows you can create a better balance between the sound of the orchestra and the reverberation of the hall, hopefully creating a fantastic sounding concert in every seat.

jonathan Berman - orchestra conductor

Interview with Jonathan Berman – Part 1: Presentation and recent activities

 

 

 

 

Marc Fuzellier-Hart: Hi Jonathan, can you introduce yourself and explain how you got into conducting ensembles and orchestras.

Jonathan Berman: Hello, I am Jonathan, an orchestral conductor. I got into music because my family is very musical, so music has always been around me. As a young kid, I learned cello and piano, and I sung which then expanded to organ, harpsichord, viols de gamba, guitar and all sorts of other instruments that I could fit around that.

However, when I was 13-14, I had some wrist injuries from playing piano too much. So I had to give up piano and cello, and actually, all my instruments for about a year. It was during this period that I really wanted to make music and discovered conducting. 

With six other friends, I put on a concert of very small choir pieces. This is when I found that conducting suited me so much better than playing instruments. Even as an instrumentalist I had always wanted to play with other people; I was fascinated not only by sound, but also by its function, its meaning and why composers made certain decisions.

So I found conducting very early on and whilst I was at school, I did little bits of conducting. I was incredibly lucky to essentially go to a specialist music school. There were lots of really good musicians. We had orchestras and choirs that I conducted, then during the summer holidays I would go on conducting courses.

After school, I went to a conservatoire in Holland. I did a Bachelor’s and a Master’s both in conducting, which was an amazing education. I studied with one main teacher for six years, and it was really an old-school apprenticeship more than a college education as I was working as his assistant.

I would often travel with my teacher to his concerts and rehearsals, and it was great seeing the way one conductor would work differently with different orchestras, express things differently, in different countries and in different repertoires.

Now [December 2020] is obviously a very bizarre moment, but in normal times I am lucky enough to travel around the world, conducting orchestras, operas, small groups as well. I do a lot of contemporary music. I really believe that our musical tradition needs to be a living one that connects the past and the present.

 

MF: Yes, it is great to be able to speak to the composer and ask them the way they ideally want the music to be played. And then you can add your own taste and colour.

JB: Absolutely, we spend hours thinking “I wonder what Beethoven meant here”. When you work with living composers like James Macmillan, Mark Turnage or George Benjamin, and you go  “what do you mean by this here?” and you can have an answer. I love that, and I learn so much from the composers I work with. I think it is hugely important to work with people who challenge the boundaries of our creative tradition. 

 

MF: What have been your activities during lockdown?

JB:  Just before lockdown started, I had my first set of cancellations and there was a huge amount of anxiety for all performers. Out of this moment came my first lockdown project – an initiative called ‘ Stand Together Music ’ which I set up with my sister, Imogen, who is very involved in the popular music world. For the first 100 days of lockdown we published a list of every cancelled concert, both classical and non-classical along with daily playlists on Spotify using recordings by cancelled artists.

We ended up curating 12,149 tracks, over 1000 hours of music created by over 10,000 composers/ performers/ orchestras/ bands who all suffered from cancellations. Our aim was to try and encourage people to stream music during (and after) the lockdown consciously so that in some small way we could divert the streaming revenue back to the artists who were suffering cancellations. We also did special features on all UK orchestras, opera houses and many european and international establishments as well.

My other big lockdown project was about making 9 films of and about classical music (which we talk about elsewhere in this blog) – which were nominated and even won some prizes at film festivals – one, unbelievably, for best cinematography!

Jonathan Berman - The Franz Schmidt Project

I was also lucky enough to get into the recording studio just before the first lockdown to start recording a cycle of the complete symphonies of the Austrian composer Franz Schmidt. This is part of a bigger project I have set up – ‘The Franz Schmidt Project’ – to promote his music leading up to his 150th Birthday in 2024.

The backbone of the project will be the complete cycle of his symphonies which I am recording with the BBC National Orchestra of Wales, and through which we will promote Schmidt’s music along with interviews, live performances (throughout the world), radio shows, television broadcasts and talks.

Recording is a fascinating acoustical challenge because microphones don’t pick up sound in the same way ears do – and orchestral sound is a pretty complex sound to begin with!

So in essence, you have three variables on the sound; the playing of the orchestra, the acoustics of the hall and the placing, number, type and balance of microphones.

I am very much a believer in using as few microphones as possible (I think still some of the best sounding recordings ever are the old Mercury Living Presences recordings from the 50’s using three, occasionally only one, Schoeps M201 microphones – even for huge orchestras). Whilst we did have more than three microphones for this recording, the process was the same whereby we tried to get the sound and balance in the room and then replicate that sound through the microphones. We recorded in the beautiful Hoddinott Hall in Cardiff.

 BBC National Orchestra of Wales - Jonathan Berman -  The Franz Schmidt Project

Interestingly my relationship with the BBC National Orchestra of Wales goes back over 10 years and I was at the opening of the hall. It is fascinating to hear how the sound of the hall has changed over the years. It has softened over time. I have noticed the same effect at the Ozawo Hall in Tanglewood (another wooden hall in the USA) whereby each year the sound feels warmer and in particular the upper frequencies soften.

Back to Cardiff, the Hoddinott hall has some wonderful flexible acoustics. On the first day of rehearsals, we found the hall (both on stage and in the recording booth) a little too dry and small for the expansive soundscape of the Schmidt symphony, and so we were able to open some doors, right at the top of the hall to increase the physical volume of the hall until we got a sound that we liked through the microphones.

 

MF: Are you involved in any activities around educating people for music or raising people’s sensitivity to music?

 JB: I don’t have an official position of teaching but I absolutely love to teach conducting. As for raising sensitivity to music, one of our great roles as musicians is to bring people into music and show them what joy there is in actively listening to music.

You know, we have a thousand different types of music and ways to listen depending on the functions in our life. We put music on when we go to the gym, we put music on to sleep, to cover awkward silences in a conversation or just as some kind of background. That is all wonderful. I use music like that. But there is this thing which I love, it can be any genre, you sit, you focus and you engage actively your imagination, your sensitivity; you engage and commit yourself fully in following the music. 

I love bringing people into this way of listening and this world of music.  I love showing them different types of music, different pieces of the same composer that they know or letting them see some aspects of a certain piece of music. It really gets me going and I want to share that with people. Musical understanding is not something that you either have or don’t have – a clandestine group of those in the know. There are many pieces, composers which at first hearing I didn’t understand or didn’t even like. But through time, through multiple listenings, through listening to others talk about this music, I have come to absolutely adore these pieces and composers.

I recently filmed a series called Postcards from Vienna, where I talk about viennese music. Along with an amazing woman called Emily Ingram (co-founder and CEO at Onjam), we made four episodes of this documentary about classical music along with five other classical music movies. They are not just video performances, but videos that somehow visually draw people into the underlying structures, images, ideas, associations, illusions within a piece of music. All of these movies were trying to create, in different ways, environments for people to get closer to this active way of listening and interacting with music.

Jonathan Berman - Postcards from Vienna

The first we did, during lockdown, was the Goldberg Variations with a Dutch string trio. They were combined with Sir Simon Russell Beale reading texts, all about solitude and photographs from the artist Kristina Feldhammer.

Then we did a video of Stravinsky Septet where we created new artworks inspired by artists who connected with the period of Stravinsky’s work. Natalia Goncherova, Sonya Delauney and Lyubov Popov for the first ‘Ballet Russe’ movement, Mark Rothko for the middle movement and then we recreated the process of painting Lee Kransner Abstract Expressionist painting.

I wanted to show and to visualise that for Stravinsky in the Septet. He is developing and discovering formal processes and putting them either onto something old fashioned or something really new. However, he is not writing a piece of music about the formal processes, but in fact the opposite. He is using the formal process to create character, emotion and direction – just music!

My idea is that, without actually educating people, without being a teacher and say “this is what happens, you go and learn it”, you can provide them a key into something that is not simplistic but nuanced and complex. You don’t have to talk or express it with complexity.

I tried in the movies to realise these ideas using the visual elements of films. Pictures say a thousand words. In the documentary series of Postcards from Vienna (where I talk about music), I don’t use musical terms or long words. I try to visualise the musical processes and the decisions of the composers.

8 reasons why you should engage acoustic designers very early on mass timber projects

 

 

 

 

Mass timber constructions pose particular challenges for acoustic engineers. 

This is why the acoustic design for mass timber buildings needs to be considered earlier than on more traditional buildings. Doing this can have positive consequences on the budget, the comfort of the occupiers and the sustainability of the building. 

This post gives you 8 reasons why you should follow this advice.

  01

To take account of the weaknesses at low-frequencies  

Timber constructions are known for their sound insulation weaknesses at low frequencies. This usually leads to a reduction of comfort for the occupiers.

A common problem in timber constructions is the disturbing audibility of people walking on floors.  

Depending on the country, the local building regulations might not consider the right frequency range. Baring this in mind, the acoustic designer is likely to recommend the extension of the design brief for some parts of the building. For more details on this topic, check Why we need to think beyond building regs for the sound insulation of CLT constructions .

Be aware of the consequences though! Setting these types of extensions can lead to needing more materials, implementing specific design methods and probably needing more space.

Therefore, you need to consider this as early as possible in the planning to avoid any unexpected loss of space or increase of the construction cost.

Although, there is always room for optimisation, which the acoustic designer will help you with. 

02

To know how much mass is needed from the start

 

Along with cavities and decoupling methods, the acoustic designer relies on adding mass to improve the sound insulation performance of the partitions. 

Timber structures being very light, you really can’t avoid needing to add mass to most separations. At least, those that are acoustically rated. 

Adding mass could result in a structure significantly heavier than originally planned.

Not taking onboard the need for a minimum of mass early enough in the design, could lead to surprises during the later design stages. To the point of having to re-design the structure and maybe the foundations to take account of the extra load. 

03

To decide early on the reliance of dry and wet solutions 

If not for sustainability and speed of construction, acoustic consultants would advise implementing wet solutions in timber buildings (i.e. using concrete and plaster generally).

The advantages are:

  • they are made with dense materials that are very useful in adding  mass to the constructions.
  • because the materials are dense, you can minimise the thickness of the layers and lose less space in the buildings.
  • they can increase the internal vibration damping and the stiffness of the separations.
  • to a certain extent, they can fill the gaps between the timber elements.

However, dry solutions are preferred for timber buildings because the materials involved are generally less harmful to the environment, quicker to install and lighter. Three strengths mass timber constructions are very well known for.

The design techniques, materials and products to control the sound insulation with wet and dry solutions can be very different. To the point that changing from wet to dry (and vice-versa) in the middle of a design can lead to re-budgeting and sometimes re-designing

So it is best to decide as early as possible, with the acoustic consultant, whether the design will rely on wet and/or dry construction methods.

04

To optimise the building layout and stay on budget 

Let’s face it: controlling the transmission of sound between spaces in timber buildings is challenging!

To comply with the design brief, the acoustic consultant will advise for more mass, more materials and more products. All of these are likely to increase construction cost.

To minimise this and stay on budget, you can work with the acoustic consultant by optimising the building layout to separate and disconnect the loud and sensitive spaces as much as possible. 

This way, you will reduce the reliance of expensive measures to control the sound transmission between the spaces. 

Working on the building layout can also help you minimise the embodied carbon of the building. See Reason 7.

 

Note: The above is not just applicable to timber buildings but to any type of building.

05

To plan for the right amount of space

As discussed above, sound insulation design is based on associating mass, decoupling methods and cavities. 

But because timber is a light material, the acoustic consultant compensates on the two latter leading separations to be generally thicker and wider.

Also, the materials used in dry solutions are not always as dense as those in used in wet solutions. So if you design your building with dry solutions and need a minimum amount of mass, it is likely that the heavy layers will need to be rather thick compared to those of wet solutions.

By knowing all the above, you can plan early for enough space between the rooms and avoid having to compromise on room size later down the line.  

06

The acoustic and structural engineers need to work together early

For mass timber projects, the acoustic design should ideally be considered at the same time as the structural design. 

This is not just because more mass creates a higher load as discussed in Reason 2. It is also to work on suitable design methods to control the vibrations transmitted to/between the building elements.

 

Note: Vibrating elements can re-radiate audible sound. But it depends on a few different factors. 

 

The acoustic and the structural engineers could work together on:

 

  • the connections between the elements: depending on the fixing method, more or less vibrations are transmitted between the timber elements. The same goes with the way the elements are in contact with each other. 
  • cavity breaks: they can be efficient at controlling vibrations, but might not always be possible to have for structural and cost reasons.
  • stiffening some separations: different methods exist to do this. You could either add more mass, connect stiffer elements with a certain degree of bonding or also reduce the spans/spacing between the structural elements.

Why is stiffening the separations important? Because it is one way to increase their sound insulation performance at low frequencies. 

07

To minimise the embodied carbon and increase the sustainability of the building 

Acoustic design is not very environmentally friendly.

It often relies on materials that are not sustainable or require a certain amount of energy (emitting CO2) to be produced. 

In other words, acoustic design has the potential to screw up your plans for net-zero carbon!

If you start working early with the acoustic consultant, he/she can help you minimise this by working on:

 

  • the building layout. As discussed in Reason 4, optimising the building layout is likely to reduce the use of mass, materials and products to comply with the design brief. This process can therefore have a positive impact on the embodied carbon of the building.
  • implementing sustainable design methods. The main thing here is to go for dry solutions as much as possible. They use more materials and products that are sustainable and require less energy to be produced. As discussed, in Reason 3, implementing dry solutions is a choice to make as early as possible. 
  • using sustainable products.  This choice doesn’t necessarily need to be made early in the design. Although, you might need to consider some products early as extra tests could be required. See the following paragraph for more details.

08

To plan for further possible testing

Depending on the situation, the acoustic consultant might recommend testing specific solutions because:

 

  • They have never been tested.
  • They have been tested but some performance data or details are missing.
  • They have been tested, but not under the right conditions.

 

This is more likely to happen for timber buildings, especially when the solutions are related to sound insulation design.

It is known that, in controlling the sound insulation within timber buildings, some materials have a different efficiency on timber structures than on masonry structures.

In other words, if a material has a certain performance on a masonry construction, it doesn’t mean it will achieve the same performance on a timber construction. So you could need to re-test the material on a timber construction. (resilient layers, that help control the impact sound insulation of floor constructions, are probably the best example).

Also, a material/product might have already been tested, but the data or the testing methods are limited.

It is usually the case for the frequency range considered that doesn’t go below 100 Hz, when acoustic designers need data down to at least 50 Hz (if not 20 Hz).

For impact sound insulation testing, it is good to use a calibrated impact ball (as well as the traditional tapping machine) which is not often used to test masonry floor constructions. 

Finally, we know that the sound insulation performance of mass timber elements can dramatically vary with the mounting conditions (i.e. fixings, spans and also spacing between structural elements). If the proposed mounting conditions hugely differ from those already tested, it might be necessary to undertake more tests (in a lab or on-site).

 

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Sound reverberation – Part 2: Specialist indices 

 

 

 

 

If you design a new performance space, you want to know how the musical or speech-based activities will be heard.

Or similarly, you might want to establish the acoustic conditions of an existing performance space.

As part of the assessment, you generally need to ask yourself: 

  • is the space going to be too dead or too live for the type of performances planned?
  • are the performances going to be clear and/or intelligible to the audience?
  • are performances going to sound too quiet or too loud … or just right?
  • is the space (especially during musical performances) going to sound too dry or too boomy? 

Part 2 here goes through some specialist acoustic indices that help to objectively answer the above questions.

These indices are:

  • the Early Decay Time (EDT).
  • the Sound Strength (G).
  • the Objective Clarity (C80) or Definition (D50).
  • the Early Lateral Fraction Energy (LF).

Rather than showing very technical data and complicated formulas, it intends to shed some light on which parts of the sound reverberation are used to assess the acoustic qualities of a space.

To better understand this section, you could read Sound reverberation – Part 1: Basics first. It explains what the sound reverberation is, how it is measured and what the reverberation time index is.

 

Note: this post is based on the following documents:

  • Auditorium Acoustics and Architectural Design – Mike Barron;

  • Concert halls and Opera Houses – Music, Acoustics and Architecture – Leo Beranek

  • ISO 3382-1: 2009 – Acoustics — Measurement of room acoustic parameters — Part 1: Performance spaces

 

 

 

 

 

Early decay time (EDT)

 

 

As its name says, the EDT is a measure of how fast (or not) the early sound energy decreases in a room. The quicker the early reverberation dies, the shorter the EDT.

Technically, it is based on measuring how long the early energy takes to decay by 10 dB (excluding the direct sound from the source).

The EDT is very often used for the (re)design of music performance venues and relates to the perception of acoustic reverberance.

 

 

 

 

 

 

 

 

 

 

 

Early decay time - 10 dB - sound reverberation - sound energy decay
Calculation of Early Decay Time

 

 

 

 

 

In the table below, you can see some examples of preferred EDT values (in seconds) for different types of musical performances.

Types of spacesPreferable Early Decay Time (EDT) values
Symphonic repertoire
(over 1400 seats)
2.2 s EDT500-1000Hz* 2.6 s
Chamber music
(under 700 seats)
1.9 s EDT500-1000Hz* 2.3 s
Opera
(over 1200 seats)
1.5 s EDT500-1000Hz* 1.9 s
*EDT500-1000Hz : average of Early Decay Time at 500 Hz and 1000 Hz (in unoccupied conditions)

 

Examples of preferable Early Decay Time values

You can see that the EDT values are shorter for opera performances than for chamber music and symphonic music performances.

This means that you want the early reverberation to die quicker for opera music than for chamber music and symphonic music.

 

Sound Strength (G)

 

 

The Sound Strength (G) relates to how loud (or quiet) sound sources might be perceived in a room. In a way, it characterises the amplification power of the room. 

You can measure G using an omnidirectional sound source and compare:

  • the acoustic energy of that source at a given point, against;

 

  • the energy of the same source, located 10m away from the receiving position, in an environment with no sound reflecting surfaces (conditions found in anechoic chambers).

 

 

 

 

 

 

Sound Strength - G - omnidirectional source - sound reverberation - free field - sound energy
Calculation of Sound Strength (G)

The sound strength is measured in dB and usually ranges between 0 and +10 dB in performance venues.

In the table below, you can see some examples of preferred values for different types of musical performances.

Types of spacesPreferable Sound Strength (G) values
Symphonic repertoire
(over 1400 seats)
1.5 dB Gmid* 5.5 dB
Chamber music
(under 700 seats)
9 dB Gmid* 13 dB
Opera
(over 1200 seats)
-1 dB Gmid* 2 dB
*Gmid : average of Sound Strength at 500 Hz and 1000 Hz

 

 

Examples of preferable Sound Strengths values

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

What do these values tell us?

 

The preferred values are mostly positive. This means spaces need to amplify the sound of performances. Which makes sense, especially for the more remote seats where you also want to hear the quieter instruments and sound details of the performances.

The preferred ranges have different upper limits. This shows that each type of performance has its own preferred level of amplification above which music might sound too loud and unpleasant.

The preferred values for chamber music are higher than for symphonic repertoire and for opera. This means that spaces for chamber music performances require a higher sound amplification. This makes sense because the instruments and ensembles involved in chamber music are respectively quieter and smaller than those involved in symphonic repertoire or opera.

The values presented are averages over 500 and 1000 Hz frequency bands (i.e. mid frequencies). At low frequencies (especially around 125 Hz), for symphonic music, the sound strength is preferred to range slightly higher between 3.0 and 6.0 dB. This corresponds to a preference for rather warm reverberation conditions that amplify the base sounds more than the medium sounds.

Objective Clarity (C80) and Definition (D50)

Whilst the objective Clarity (C80) helps to assess the clarity of musical performances in a space, the Definition (D50, also called Deutlichkeit) is for the intelligibility of speech-based performances.

 

 

 

Note: Musical clarity corresponds to the ability to hear the musical details

 

Both metrics are based on comparing early sound energy against the late or total sound energy arriving at a listening position. 

For the C80, you compare the energy arriving within the first 80 ms against the rest of the energy.

For the D50, you compare the energy arriving within the first 50 ms against the total of the energy.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Note: The average duration of speech sounds is around approximately 70 ms.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Objective Clarity - C80 - sound reverberation - free field - sound energy
Calculation of the Clarity (C80)

 

 

 

 

Calculation of Definition (D50)

The Definition has no unit and the preferred values range between 0.3 and 0.7. 

The Clarity is measured in dB. In the table below, you can see some examples of preferred values for different types of musical performances. 

Types of spacesPreferable Clarity (C80) values
Symphonic repertoire
(over 1400 seats)
-3 dB C80,3* 0 dB
Chamber music
(under 700 seats)
-2 dB C80,3* 2 dB
Opera
(over 1200 seats)
1 dB C80,3* 3 dB
*C80,3 : average of Clarity at 500 Hz, 1000 Hz and 2000 Hz

Examples of preferable Clarity values

 

 

 

 

 

 

 

 

 

 

 

 

 

What do these values tell us?

  • The ranges imply that a balance is desired between the early energy and the total or rest of the energy.
  • The more the early energy, the higher the values, the clearer the speech/musical messages.
  • The C80 values for Opera performances are higher than the preferred values for chamber music and symphonic music. This translates the need for more reflected sound arriving early to the listeners. This makes sense as enjoying opera performances depends on clearly understanding the musical and sung messages.
  • In comparison, the preferred values are lower for symphonic music, meaning that hearing every single musical detail is not as important and blending of musical sounds is more preferable.

Early Lateral Fraction energy (LF)

The Early Lateral Fraction energy (LF), also called the objective source broadening, considers some spatial aspects of the sound reverberation.

 

 

The metric is an objective measure of two spatial impressions:

  • a sound source becoming broader to a listener as it becomes louder.
  • the sound surrounding a listener, giving a sense of envelopment.

 

 

For musical performances, the perceived broadening of a sound source and the envelopment are both desired to create a sense of spaciousness. This is largely influenced by early reflections arriving in lateral directions to a listener. 

Hence why you calculate LF by comparing, within the first 80 ms, the sound energy arriving to the sides against the sound energy arriving in all directions.

Calculation of Early lateral fraction energy
Calculation of Early Lateral Fraction energy

 

 

 

 

 

 

 

 

 

 

 

The early lateral fraction energy has no unit. It is averaged from 125 Hz and 1000 Hz and it is generally preferred to range between 0.05 and 0.35. 

 

Other acoustic indices

Other important indices not mentioned above are:

 

 

 

 

  • Speech Transmission Index (STI): It measures the intelligibility of speech-based messages and is very often used to design Public Address Voice Alarm (PAVA) systems. Calculating the STI in a space at a specific location is complex. It depends on the speech level, the frequency content of the message, the background noise level in the space, the quality of the audio equipment and also the sound reverberation in the room;
  • Early Support (STearly) and Late Support (STlate): They are two measures of the acoustic conditions for music ensembles and concentrates on the very early sound reverberation. Stage acoustic science (based on the acoustic conditions musicians prefer to play in) has recently seen extensive progress thanks to the development of new audio reproduction techniques and computer modelling. Focus has been on the spatial and spectral (i.e. frequency related) aspects of the reverberation on stages.  

Conclusion on acoustic design

As discussed above, one key design aspect for performance venues is to study the way sound is reverberated inside.

For different listening positions, the acoustic designer works on:

 

 

 

 

 

  • controlling how fast the reverberated sound energy decreases within the space.
  • managing the natural sound amplification of the space depending on the music played.
  • controlling the frequency content of the reverberated sound.
  • finding the right balance between the early and late sound energies arriving at the listening positions.
  • controlling the directions in which the (early) sound energy arrives at the listening positions.

All the above mainly depend on the location and shape of the surfaces within the space, the volume of the space and the acoustic properties of the finishes.